Vibratory separator and screen assembly

ABSTRACT

A vibratory separator comprising a basket and a side rail for fixing at least a portion of a periphery of a screen assembly to said basket, characterised in that the vibratory separator further comprises means for pulling a screen assembly down within a periphery of a screen assembly to fix a screen assembly in said basket.  
     A screen assembly for a vibratory separator, the screen assembly comprising a support and at least one layer of screening material, wherein the screen assembly has a periphery characterised in that the support further comprises a fitting within the periphery, the fitting for receiving a means for pulling the support downwardly and fixing the screen assembly in the vibratory separator.  
     A method for fitting a screen assembly in a vibratory separator, the screen assembly comprising a support having at least one layer of mesh arranged thereon, the method comprising the steps of inserting the screen assembly into a clamping mechanism of a vibratory separator, operating the clamping mechanism wherein at least part of the screen assembly within its perimeter is pulled down to fix the screen assembly in the vibratory separator.

[0001] The present invention relates to a vibratory separator, a screen assembly for a vibratory separator and a method for fitting a screen assembly into a vibratory separator.

[0002] In the drilling of a borehole in the construction of an oil or gas well, a drill bit is arranged on the end of a drill string and is rotated to bore the borehole. A drilling fluid known as “drilling mud” is pumped through the drill string to the drill bit to lubricate the drill bit. The drilling mud is also used to carry the cuttings produced by the drill bit and other solids to the surface through an annulus formed between the drill string and the borehole. The drilling mud contains expensive synthetic oil-based lubricants and it is normal therefore to recover and re-use the used drilling mud, but this requires the solids to be removed from the drilling mud. This is achieved by processing the drilling fluid. The first part of the process is to separate the solids from the solids laden drilling mud. This is at least partly achieved with a vibratory separator, such as those shale shakers disclosed in U.S. Pat. No. 5,265,730, WO 96/33792 and WO 98/16328.

[0003] Shale shakers generally comprise an open bottomed basket having one open discharge end and a solid walled feed end. A number of rectangular screens are arranged in the basket, which are held in C-channel rails located on the basket walls, such as those disclosed in GB-A-2,176,424. The basket is arranged on springs above a receptor for receiving recovered drilling mud. A skip or ditch is provided beneath the open discharge end of the basket. A motor is fixed to the basket, which has a drive rotor provided with an offset clump weight. In use, the motor rotates the rotor and the offset clump weight, which causes the basket and the screens fixed thereto to shake. Solids laden mud is introduced at the feed end of the basket on to the screens. The shaking motion induces the solids to move along the screens towards the open discharge end. The recovered drilling mud is received in the receptor for further processing and the solids pass over the discharge end of the basket into the ditch or skip.

[0004] The screens are generally of one of two types: hook-strip; and pre-tensioned.

[0005] The hook-strip type of screen comprises several rectangular layers of mesh in a sandwich, usually comprising one or two layers of fine grade mesh and a supporting mesh having larger mesh holes and heavier gauge wire. The layers of mesh are joined at each side edge by a strip which is in the form of an elongate hook. In use, the elongate hook is hooked on to a tensioning device arranged along each side of a shale shaker. The shale shaker further comprises a crowned set of supporting members, which run along the length of the basket of the shaker, over which the layers of mesh are tensioned. An example of this type of screen is disclosed in GB-A-1,526,663. The supporting mesh may be provided with or replaced by a panel having apertures therein.

[0006] The pre-tensioned type of screen comprises several rectangular layers of mesh, usually comprising one or two layers of fine grade mesh and a supporting mesh having larger mesh holes and heavier gauge wire. The layers of mesh are pre-tensioned on a rigid support comprising a rectangular angle iron frame and adhered thereto. The screen is then inserted into C-channel rails arranged in a basket of a shale shaker. An example of this type of screen is disclosed in GB-A-1,578,948.

[0007] A further example of a known rigid support is disclosed in PCT Publication No. WO 01/76719, which discloses, amongst other things, a flat panel like portion having apertures therein and wing portions which are folded to form a support structure, which may be made from a single sheet of material. This rigid support has been assigned the Trade Mark “UNIBODY” by the applicants.

[0008] The layers of mesh in the screens wears out frequently and therefore needs to be easily replaceable. Shale shakers are generally in the order of 5 ft wide and 10 ft long. A screen of dimensions 4 ft wide by 10 ft long is difficult to handle, replace and transport. It is known to use two, three, four or more screens in a single shale shaker. A standard size of screen currently used is of the order of 4 ft by 3 ft.

[0009] U.S. Pat. No. 4,582,597 discloses a vibratory separator having a basket and channels arranged on internal faces of the basket for receiving the two sides of a screen assembly. An inflatable hose is arranged in the channels. The screen assembly comprises screening mesh laid over and fixed to a frame. The screen assembly is slid into the channels in the vibratory separator. The hose is inflated using a pneumatic fluid to force the frame of the screen assembly to assume a crowned centre, in order to reduce whipping.

[0010] GB-A-2,176,424 discloses a vibratory separator having a basket and channels arranged on internal faces of the basket for receiving a screen assembly and a clamping device. The screen assembly comprises screening mesh laid over and fixed to a frame. The clamping device comprises a frame of similar dimensions to the frame of the screen assembly. The frame has an inflatable stocking thereon, which is attached to pneumatic or hydraulic fluid supply means. When both the screen assembly and the clamping device are slid into the channels, the stocking is inflated to fix the screen assembly in the channels. There is also disclosed a clamping device having an intermediate frame member on which a tributary of the stocking is arranged. Support members are provided above and below the screen assembly so that, in use the tributary is inflated to clamp the screen assembly between the supports.

[0011] GB-A-2,176,425 discloses a vibratory separator having a basket and channels arranged on internal faces of the basket for receiving a screen assembly. The screen assembly comprises screening mesh laid over and fixed to a frame. The channels have an inflatable stocking therein for clamping the frame of the screen assembly in the channels. The screen assembly also has a stiffening rib along each of two intermediate parts of the screen assembly and the vibratory separator has a tributary of the stocking along each of two intermediate parts of the vibratory separator, such that in use, the tributaries are inflated to clamp on the stiffening ribs.

[0012] U.S. Pat. No. 4,809,791 discloses a shaker having a screen. The screen is supported on flexible transverse arch-shaped beams attached to the sides of a frame. A ram is arranged in the shaker and is attached to the centre of the flexible transverse arch-shaped beam. The ram is extended to increase the tension in the screen.

[0013] The inventor has noted that a support structure has to be very rigid and rigidly supported. In one aspect, the present invention attempts to provide an easily replaceable panel for a screen assembly of the pre-tensioned type or a partially pre-tensioned type, which is rigid and lightweight. A partially pre-tensioned type of screen assembly comprises one, two, three or more layers of screening mesh glued or otherwise attached to each other, and the layers are tensioned and are glued or otherwise attached to an apertured panel which is not rigid enough to provide a support when in use on its own in a shale shaker, but is strong enough to withstand the layers of screening material being tensioned thereover and attached to it. Bending of such a panel may occur under the tension of the layers of screening mesh, however, when the panel is placed over a support and locked in place, the layers of mesh are at a tension which is sufficient to be used in a shale shaker. It has been noted that by providing more support for the screen assembly, the frame can be lighter and retain sufficient rigidity. The frame can be made of less material, which can be transported more easily and after use, can be recycled more easily than a large heavy frame.

[0014] It is important to achieve maximum screening area in a given space and to obviate the need for mechanisms for fixing screen assemblies to shakers which blind areas of the screening material and which will decrease the screen assemblies screening capacity.

[0015] The present invention also attempts to provide a panel for a screen, which will increase the life of layers of screening material arranged thereon.

[0016] In accordance with the present invention, there is provided a vibratory separator comprising a basket and a side rail for fixing at least a portion of a periphery of a screen assembly to said basket, characterised in that the vibratory separator further comprises means for pulling a screen assembly down within a periphery of a screen assembly to fix a screen assembly in said basket.

[0017] Preferably, the means is pneumatically operable. However, the means may be hydraulically operable or be operable by both hydraulic and pneumatic means. Both means are suitable for inflating an inflatable bladder, which is preferred. The means may alternatively be mechanically operable, preferably by use of arms and gears, or hooks and tension bars or bolts, but may be any other suitable mechanism.

[0018] Preferably, the means comprises a rail for engaging the screen assembly. Advantageously, the rail is T-shaped, although may be cup shaped or the rail may be of any suitable profile or hook.

[0019] Advantageously, the means comprises an outer housing and an inner housing, the inner housing movable with respect to the outer housing for pulling a screen assembly downwardly to fix a screen assembly in the basket. Preferably, the rail is attached to the inner housing and the outer housing comprises a slit through which part of the rail passes. Advantageously, an inflatable bladder is arranged in the inner housing for moving the inner housing with respect to the outer housing. Advantageously, the outer housing has an intermediate member which passes through openings in the inner housing, the inflatable bladder arranged underneath the intermediate member. Preferably, the vibratory separator has a length and the inner housing and the outer housing extends substantially that length. Advantageously, the vibratory separator has a length and the rail extends substantially that length.

[0020] Most oilrigs provide a predetermined size of footprint for a vibratory separator, which is usually rectangular. It is important to obtain as much screening area as possible in this footprint. Accordingly, it is preferable for the basket to be rectangular having a pair opposing side walls, the side rails arranged on each of the pair of opposing side walls and the means arranged therebetween. Advantageously, the basket comprises at least one beam linking the pair of opposing sides, the means arranged on the at least one beam.

[0021] Preferably, the vibratory separator has a shoulder located within the periphery on to which the screen assembly is pulled on to, to fix a screen assembly in the basket. Advantageously, the means comprises a stationary part which forms the shoulder or land.

[0022] Preferably, the means comprises a return mechanism to facilitate release of a screen assembly, so that the screen assembly can be removed from the vibratory separator. Advantageously, the return mechanism comprises at least one return spring.

[0023] Preferably, an inflatable bladder is arranged in the side rail. The side rail may be arranged on inside walls of the basket. In a rectangular shaker, the side rails may be arranged on each side and perhaps one end wall and they may be arranged horizontally within the basket, or at an angle of up to 10° and preferably 7° to the horizontal.

[0024] The present invention also provides a screen assembly for a vibratory separator, the screen assembly comprising a support and at least one layer of screening material, wherein the screen assembly has a periphery characterised in that the support further comprises a fitting within the periphery, the fitting for receiving a means for pulling the support downwardly and fixing the screen assembly in the vibratory separator.

[0025] Advantageously, the fitting comprises a rail. Preferably, the screen assembly has a length and the rail extends the length of the screen assembly. Advantageously, the rail takes the form of a T-bar.

[0026] Preferably, the rail is a channel. The channel may have internal projections for receiving a hook or T-bar rail. Advantageously, the fitting is centrally mounted.

[0027] In one aspect, a pull down member is engageable with the fitting, the pull down member having arms, which in use, are engageable in clamping rails of a vibratory separator, such that upon activation of the clamping rails, the arms push the pull down member downwardly, pulling the support downwardly and fixing the screen assembly in the vibratory separator. Preferably, the screen assembly further comprises a rigid chassis having a plurality of ribs, each of which forms a shoulder, in use the support is pulled down and fixed on the shoulders.

[0028] Advantageously, the support comprises a panel having apertures therein. Preferably, the screen assembly further comprises a rigid chassis, the fitting formed in the rigid chassis, spaced from the panel, such that in use filtered material flows therearound. Preferably, the panel comprises folded portions. Preferably, the at least one layer of screening material is adhered to the side portions of the panel. Advantageously, the at least one layer of screening material is adhered to the area provided about each aperture. Preferably, the at least one layer of screening material comprises at least a first layer of screening mesh arranged on top of a second each other, wherein the mesh size of the second layer is the same or larger that of the first layer and has larger diameter wires making up the mesh. Advantageously, the screen assembly comprises a third layer of screening mesh. Each layer may be glued to the next with a hot melt glue or resin in a pattern which substantially corresponds with the periphery of each aperture, such that screening area is not impeded. Preferably, the panel is flexible, although may be rigid. The panel may be flexible, such that the panel can withstand any tension in the layers of screening material laid and attached thereto, (although the panel may bend a little under this tension) but is not rigid enough to support the screening material without the need for additional screen support when in use in a vibratory separator.

[0029] The present invention also relates to a vibratory separator comprising a screen assembly of the invention, the vibratory separator further comprising a basket, a vibratory mechanism and a clamping mechanism for fixing the screen assembly to the basket. Preferably, the clamping mechanism comprises a pneumatic means, and most preferably an inflatable bladder and is preferably arranged in C-shape channels arranged about the inside wall of the basket.

[0030] The present invention also relates to a method for fitting a screen assembly in a vibratory separator, the screen assembly comprising a support having at least one layer of mesh arranged thereon, the method comprising the steps of inserting the screen assembly into a clamping mechanism of a vibratory separator, operating the clamping mechanism wherein at least part of the screen assembly within its perimeter is pulled down to fix the screen assembly in the vibratory separator. Preferably, the screen assembly further comprises a pull down member, the method further comprising the step of operating the clamping mechanism depresses a pull down member, pulling intermediate parts of the panel on to the support structure.

[0031] For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which:

[0032]FIG. 1 is a perspective view of a shale shaker of a known type;

[0033]FIG. 2 is a rear end view of a first embodiment of a screen assembly in accordance with the present invention shown partly in cross-section, the screen assembly arranged in clamping rails of a shale shaker, the screen assembly comprising a panel, a support structure and a pull down member;

[0034]FIG. 2A is a cross-sectional view of the panel shown in FIG. 2;

[0035]FIG. 2B is an end view of the pull down member shown in FIG. 2;

[0036]FIG. 2C is an end view of the support structure shown in FIG. 2;

[0037]FIG. 2D is a top plan view of the panel shown in FIG. 2A fitted to the pull down member shown in FIG. 2B;

[0038]FIG. 2E is an underneath view of the panel shown in FIG. 2A fitted to the pull down member shown in FIG. 2B;

[0039]FIG. 2F is a top plan view of the support structure as shown in FIG. 2C;

[0040]FIG. 2G is an enlarged top view of part of the panel shown in FIGS. 2 and 2D;

[0041]FIG. 2H is a top plan view of a blank used in the construction of a panel in accordance with the present invention;

[0042]FIG. 2I is a template used in the construction of the panel of the present invention;

[0043]FIG. 3 is a perspective view of a second embodiment of a screen assembly in accordance with the present invention, the screen assembly arranged in a shale shaker in accordance with the present invention, the shale shaker having side clamping rails and a central clamp;

[0044]FIG. 3A is a rear end view of the shale shaker and screen assembly shown in FIG. 3;

[0045]FIG. 3B is a rear end view of part of the central clamp shown in FIG. 3;

[0046]FIG. 3C is a side view of the part of the central clamp shown in FIG. 3;

[0047]FIG. 3D is a view in cross-section of the part of the central clamp taken along line 3D-3D of FIG. 3C;

[0048]FIG. 3E is a top view of the part of the central clamp of FIG. 3B;

[0049]FIG. 3F is a top plan view of the screen assembly shown in FIG. 3, with a portion of screening material cutaway;

[0050]FIG. 3G is a perspective view of the rear end and underneath of the screen assembly shown in FIG. 3;

[0051]FIG. 3H is a side view of the screen assembly shown in FIG. 3;

[0052]FIG. 3I is a view in cross-section taken along line 3I-3I of FIG. 3F;

[0053]FIG. 3J is a view in cross-section taken along line 3J-3J of FIG. 3F;

[0054]FIG. 3K is a rear end view of the screen assembly shown in FIG. 3;

[0055]FIG. 3L is a rear end view of the screen assembly shown in FIG. 3, arranged in the side clamping rails and the central clamp of the shale shaker of FIG. 3, the central clamp deactivated;

[0056]FIG. 3M is a rear end view of the screen assembly shown in FIG. 31 arranged in the side clamping rails and the central clamp of the shale shaker of FIG. 3, the central clamp activated;

[0057]FIG. 4 is a scrap rear end view of a part of a further embodiment of a screen assembly in accordance with the present invention, shown with a hook rail of a central clamp of a vibratory separator; and

[0058]FIG. 5 is a scrap rear end view of a part of a further embodiment of a screen assembly in accordance with the present invention, shown with an alternative central clamp.

[0059] Referring to FIG. 1, a prior art shale shaker 1 is shown with a screen assembly 2 mounted therein. The screen assembly comprises a frame (not shown) and a layer of screening material tensioned over the frame. The screen assembly 2 is mounted in a basket 3, which has: an open bottom, for allowing fluid and small particles to pass into a receptacle (not shown) therebeneath; a feed end at which material to be screen is introduced (to the right of the drawing) and a mouth (to the left of the drawing) for allowing large particles to pass into a skip or ditch. The basket 3 is mounted on springs 4 (only two shown; two as shown are on the opposite side) which are supported on a structure 6. The basket 3 and the screen assembly 2 mounted therein is vibrated by a motor 5 interconnected with vibrating apparatus 8. The vibrating apparatus 8 may be of the type which comprises an unbalanced weight on the end of the motors drive shaft. Elevator apparatus 7 provides for raising and lowering of the basket end. Typically the basket will be in a “climb the hill” position so that a pool of liquid is maintained at one end within the basket.

[0060] Referring to FIG. 2, there is shown a screen assembly, generally identified by reference numeral 100. The screen assembly 100 comprises a panel 101, a support structure 102 and a pull down member 103. In use, the panel 101 would have at least one layer of screening material adhered or otherwise attached thereto. Typically, each layer of screening material comprises a layer of wire mesh. Typically, the panel 101 would have three layers of wire mesh lying one over the other, the lowermost layer of wire mesh having larger openings and larger wires. In use, the screen assembly 100 is arranged in clamping rails 104 and 105 of a shale shaker.

[0061] Referring to FIGS. 2A, 2D and 2G, the panel 101 is made from a 1.5 mm mild steel plate. The panel 101 comprises an area 106 provided with a plurality of apertures, a left side portion 107 provided with no apertures and a right side portion 108 provided with no apertures. The plurality of apertures in area 106 comprises a plurality of triangular apertures and a plurality of circular openings.

[0062] The panel 101 is formed from a blank shown in FIG. 1H. Lines 110 and 111 and fold lines 112 and 113 indicate the boundary of area 106 which will be provided with the plurality of apertures. The area 106, the left side portion 107 and right side portion 108, all lie in the same plane to form a flat top surface. Left side portion 107 and right side portion 108 extend the entire length of the panel 101. Wing portions 114 and 115 approximately lam wide extend the entire length of the panel 101. The wing portions 114 and 115 are folded downwardly to stand approximately at right angles to the top surface. The forward end of the panel 101 has a forward end portion 116 extending the width of the panel 101 and is folded downwardly along fold line 112 to be perpendicular to the top surface of the panel 101. The trailing end of the panel 101 has a rear end portion 117 folded downwardly along fold line 113, such that the rear end portion 117 lies perpendicularly to the top surface of the panel 101. A screen interface, such as those disclosed in PCT Publication Number WO 01/97947 may be used at both the front and rear of the panel. The folded wing portions 114 and 115 and the folded end portions 116 and 117 meet at their respective side edges, at which they may be welded together, soldered or otherwise joined.

[0063] The area 106 of the blank shown in FIG. 2H has a plurality of apertures including a plurality of triangular apertures and a plurality of circular apertures formed therein. One of the triangular apertures is identified by reference numeral 118 and one of the circular openings is identified by reference numeral 119. The triangular aperture 118 is formed by first punching, laser cutting, sawing, drilling, milling or casting the blank with an opening 120, in the shape shown in the template shown in FIG. 1I. The shape comprises three semi circular ends 121, 122 and 123 each arranged within and close to where a respective vertex 124, 125 and 126 of the triangular aperture 118 is to be formed, as shown in FIG. 1G; and a small triangular opening 127 concentric with the triangular aperture 118 to be formed and slots 128, 129 and 130 link the semi circular ends 121, 122 and 123 to form structural portions 131, 132 and 133. The structural portions 131, 132 and 133 are folded downwardly along fold line 134, over a form tool (not shown) having a similar profile to the fold line 134. The structural portions 131, 132 and 133 are folded by the form tool to an angle of approximately 65° to the surface of the panel 101 to form edges 131 a, 132 a, and 133 a. The areas 135, 136 and 137 of panel 101 bounding the semi circular ends 121, 122 and 123 are also folded downwardly.

[0064] Referring back to FIGS. 1D and 1G, triangular apertures, such as triangular aperture 118, are arranged in ten full sets of rows in the panel 101 and one further row of a set. A first set 138 comprises a first row 139 having a rearwardly pointing triangular aperture 118 and a forwardly pointing triangular aperture 140 adjacent thereto, such that folded structural portion 132 and a folded structural portion 141 of the forwardly pointing triangular aperture 140 form a panel rib 142, approximately 2.3 mm wide. An apex 143 of the forwardly pointing triangular aperture 140 is rearwardly offset by approximately 2.3 mm from a base edge 131 a of the rearwardly pointing triangular aperture 118. The first row 139 comprises twelve forwardly pointing triangular apertures interspaced by twelve rearwardly pointing triangular apertures. The first set 138 also comprises a second row 144, which is a mirror image of the first row 139 about line A-A. A structural portion 145 of forwardly pointing triangular aperture 140 of the first row 139 and a structural portion 146 of a rearwardly pointing triangular aperture 147 of the second row 144, form a panel rib 148. The underside of panel rib 148, the structural portion 145 and the structural portion 146 form a channel. The panel rib 148 is in line with panel ribs 149 to 159 in the first set 138, the undersides of which form a channel which extends the width of the panel 101. Circular opening 119 is drilled, punched, laser cut or otherwise formed in the panel 101 between vertices 125, 160, 161 and 162 of rearward pointing triangular aperture 118, forward pointing triangular aperture 163, forward pointing triangular aperture 140 and rearward pointing triangular aperture 147 respectively. A segment opening 164 arranged between rearward pointing triangular aperture 118, forward pointing triangular aperture 163 and circular hole 119 is punched, laser cut or otherwise formed in the panel 101, having a straight portion following line 110 of the blank, shown in FIG. 1H and a curved portion extending toward the rearward pointing triangular aperture 118, forward pointing triangular aperture 163 and circular opening 119.

[0065] Similarly, circular opening 165 is drilled, punched, laser cut or otherwise formed in the panel 101 between vertices 166, 167, 168, 169, 170 and 171 of forward pointing triangular aperture 140, rearward pointing triangular aperture 172, forward pointing triangular aperture 173, rearward pointing triangular aperture 174, forward pointing triangular aperture 175, and rearward pointing triangular aperture 147 respectively.

[0066] Referring to FIG. 2A, the panel 101 further comprises two inverted T-shape rails 176 and 177, arranged longitudinally from the forward end portion 116 to the rear end portion 117. The inverted T-shape rails 176 and 177 are spaced at intermediate the left side and right side of the panel 101, preferably, each located at a third of the width between the left and right sides. The inverted T-shape rails 176 and 177 are welded to the panel 101 at the root of the T.

[0067] Referring to FIGS. 2, 2B, 2D and 2E, the pull down member 103 comprises twelve substantially identical ribs 178 to 189. Rib 178 is made from 3 mm steel plate. The rib 178 has a body portion 190, a left arm 192 extending along a top of the body portion provided with a head 193; and a right arm 194 extending along a top of the body portion provided with a head 195. A left side runner 196 is welded to the head 193 and a right side runner 197 is welded to the head 195. The left side runner 196 and right side runner 197 extend the entire length of the screen assembly 100. Two receiving rails 198 and 199 are welded in respective recesses 200 and 201 in the body portion 190, intermediate the rib 178, preferably, each located at a third of the length of the rib from either end thereof. The receiving rails 198 and 199 are of a C-shape cross-section to receive the inverted T-rails 176 and 177. The eleven other ribs 179 to 189 have corresponding heads, which are welded at intervals therealong to the left side runner 196 and right side runner 197 respectively and corresponding recesses in which receiving rails 198 and 199 are welded. The rib 178 is at a rear end; rib 179 is arranged slightly less than two intervals from rib 178; rib 180 is arranged two intervals from rib 179; rib 181 is arranged two intervals from rib 180; rib 182 is arranged two intervals from rib 181; rib 183 is arranged two intervals from rib 182; rib 184 is arranged two intervals from rib 183; rib 185 is arranged two intervals from rib 184; rib 186 is arranged two intervals from rib 185; rib 187 is arranged two intervals from rib 186; rib 188 is arranged two intervals from rib 187; rib 189 is arranged slightly less than one interval from rib 187. An interval being equal to the width of a row 139, 144 in the panel 101; and two intervals being equal to the width of a set of rows 138 in the panel 101.

[0068] Referring to FIGS. 2, 2C and 2F the support structure 102 comprises twelve substantially identical support ribs 202 to 213. Support rib 202 is made from 3 mm steel plate. The support rib 202 has a body portion 214, a left arm 215 extending from the body portion having a bottom face 216, and a right arm 217 having a bottom face 218. A left side support bar 219 is welded in recess 220 in the left side of the body portion 214 and a right side support bar 221 is welded in recess 222 in a right side of the body portion 214. The left side support bar 219 and right side support bar 221 extend the entire length of the screen assembly 100. Two recesses 223 and 224 in the body portion 214 are located intermediate the ends of the rib 202, preferably, each located at a third of the length of the rib 214 from either end thereof. The top edge 225 of the support rib 202 is provided with a chamfer. The eleven other ribs 203 to 213 are welded into corresponding recesses 220 and 221, at intervals along the left side support bar 219 and right side support bar 221 respectively. The support rib 202 is at a rear end of the screen assembly 100. Support rib 203 is arranged one interval from support rib 202; support rib 204 is arranged two intervals from support rib 203; support rib 205 is arranged two intervals from support rib 204; support rib 206 is arranged two intervals from support rib 205; support rib 207 is arranged two intervals from support rib 206; support rib 208 is arranged two intervals from support rib 207; support rib 209 is arranged two intervals from support rib 208; support rib 210 is arranged two intervals from support rib 209; support rib 211 is arranged two intervals from support rib 210; support rib 212 is arranged two intervals from support rib 211; support rib 213 is arranged two intervals from support rib 212. An interval being equal to the width of a row 139, 144 in the panel 101; and two intervals being equal to the width of a set of rows 138 in the panel 101.

[0069] The screen assembly 100 is assembled by sliding the inverted T-shape rails 176 and 177 of the panel 101 into the receiving rails 198 and 199 of the pull down member 103. The pull down member 103 is located in the support structure 102. The ribs 178 to 189 are inserted into support ribs 202 to 213. End ribs 178 and 189 are inserted inside support ribs 202 and 213. Rib 179 is arranged one interval from support rib 203 and one interval from support rib 204; Rib 180 is arranged one interval from support rib 204 and one interval from support rib 205; rib 181 is arranged one interval from support rib 205 and one interval from support rib 206; rib 182 is arranged one interval from support rib 206 and one interval from support rib 207; rib 183 is arranged one interval from support rib 207 and one interval from support rib 208; rib 184 is arranged one interval from support rib 208 and one interval from support rib 209; rib 185 is arranged one interval from support rib 209 and one interval from support rib 210; rib 186 is arranged one interval from support rib 210 and one interval from support rib 211; rib 187 is arranged one interval from support rib 211 and one interval from support rib 212; rib 188 is arranged one interval from support rib 212 and one interval from support rib 213 and slightly less than one interval from rib 189. The support ribs 203 to 212 align underneath the lines of panel ribs 226 to 235 between structural portions folded to form the edge of the apertures. Support rib 202 aligns with line of panel ribs 236 and support rib 213 aligns with line of panel ribs 237.

[0070] The panel 101 has at least one layer screening mesh arranged thereon. The layer of screening mesh may be tensioned and adhered to the outer perimeter of the panel 101 and to all of the panel ribs. Preferably, at least three layers are applied. The layers may be of the same mesh grade or of different mesh grades. Preferably, a layer of screening mesh having larger openings and larger wires lies beneath layers of fine mesh.

[0071] In use, the screen assembly 100 has layers of mesh (not shown) arranged on the panel, and is slid into clamping rails 104 and 105 of a shale shaker. The clamping rails 104 and 105 comprise a C-shape rail 240 and 241 having a bottom surface 242 and 243 on which the support structure 102 of the screen assembly 100 rests. The C-shape rail 240 and 241 also has a pneumatically inflatable bladder 244 and 245 fixed to an upper part 246 and 247 of the C-shape rail. The inflatable bladder 244, 245 is inflated which pushes down on side portions 107 and 108 of the panel 101, pushing the panel 101 on to the top edges 225 of the twelve supporting ribs 202 to 213. The pneumatic bladder also engages side runners 196 and 197 of the pull down member 103, which pushes the pull down member 103 downwardly, pulling the inverted T-shape rails downwardly within recesses 223 and 224. The panel 101 is pulled down along the inverted T-shape rail to pull the panel 101 down on to the supporting ribs 202 to 213. The supporting ribs 202 to 213 lie underneath the circular openings 119, 165, which partially blinds the openings, however, this is not significant as the ribs are below the level of the top surface of the layers of screening mesh.

[0072] The downwardly folded wings 114 and 115 of the panel 101 locate over the ends of the supporting ribs 202 to 213 and forward end portion 116 and rear end portion 117 are located over supporting rib 213 and 202.

[0073] Drilling mud having solids entrained therein is introduced at a feed end of the shale shaker and is shaken along the layers of mesh on the screen assembly. Fluid and small particles pass through the layers of mesh on the screen and through the triangular apertures and the circular openings in the panel 101 and past the pull down member 103 and the support structure 102 and into a receiver (not shown). The larger solids pass over the layers of screening material and out of a discharge end of the shale shaker into a skip or ditch.

[0074] The most likely component to wear out or fail first, is the layers of screening material arranged on the panel 101. The screen assembly 100 is removed from the C-shape rails 104 and 105. The panel 101 having layers of worn out screening mesh thereon and the pull down member 103 may be lifted from frictional engagement with the support structure 102. The panel 101 is slid out from receiving rails 198 and 199 and replaced with a new panel having layers screen mesh thereon. The rails of the new panel are slid into the receiving rails of the pull down member 103. The pull down member 103 with the new panel is placed on the original support structure 102 and slid back into the shale shaker.

[0075] It is envisaged that the panel may be of any known type, such as 1.5 mm to 3 mm steel, aluminium or plastics material plate with a multiplicity of apertures punched therein or perforated plate, not having folded edges to the apertures. The apertures may be oblong, pentagonal, hexagonal, heptagonal, octagonal, circular or any other shape.

[0076] The layers of screening material used in any of the embodiments shown herein and in any embodiment of the invention, may be pre-tensioned and adhered, bonded or otherwise attached to the panel. The layer of mesh may be bonded using a heat activated powder.

[0077] Referring to FIGS. 3 and 3A, there is shown a screen assembly 400 arranged in a shale shaker 300. The shale shaker 300 comprises a basket 301 having solid walled sides 302 and 303 and an open bottom 304. C-shape rails 305 and 306 are located on the inside of solid walled sides 302 and 303 respectively. The C-shape rails 302 and 303 may be welded or otherwise attached or formed integrally with the solid walled sides 302 and 303. The C-shape rails may be arranged parallel with the top and bottom of the basket, or may be arranged at an angle thereto, such that the screen assemblies arranged in the C-shape rails 305 and 306 lie at an incline from the feed end to the mouth of the basket. This incline may be between 2° to 10° and may be 7° and the incline may not be continuous along the length of the basket of the shale shaker. The rake of the basket may also be adjustable by use of an elevator apparatus, similar to the elevator apparatus shown in FIG. 1.

[0078] An end wall (not shown) at a feed end of the basket 301 may also be provided with a C-shape rail (not shown), or other form of sealing member on to which an end of a screen assembly 400 may seal against. The C-shape rails 305 and 306 are each provided with an inflatable bladder 307 and 308 such as an inflatable hose or stocking. The bladder 307 and 308 may be made from a rubber or synthetic rubber and has a hollow interior for receiving a pneumatic or hydraulic fluid.

[0079] Rigid steel tubes 309 and 310 and further rigid steel tubes (not shown) spaced along the bottom of the basket 301 link the two sides 302 and 303. A central clamp, generally identified by reference numeral 311, is fixed to the centre of the rigid steel tube 309 by solid steel plates 312, 313. The central clamp 311 is also fixed to the other rigid steel tubes 310 and (not shown) using similar steel plates (not shown). The central clamp 311 comprises a housing 314, which extends substantially the entire length of the basket 301. The housing 314 is arranged to be parallel to the C-shape rails 305 and 306. The housing 314 may extend from the mouth of the basket and slightly further than the C-shape side rails 305 and 306. The outer housing 314 has two sidewalls 315 and 316 welded to a bottom plate 316 a. Each of the two sidewalls 315 and 316 has an upper portion 317 and 318 folded at right angles to form a shoulders and a slot 319 therebetween. The shoulders are located at the same level as the bottom of the C-shape rails 305 and 306, but may be at a level which is slightly higher (may be up to 10 mm, but preferably no more than 5 mm) or slightly lower (may be up to 10 mm, but preferably no more than 5 mm). A plate 320 extends substantially the entire length of the housing 314 within the housing 314. The plate 320 has opposing sides 321 and 322. Each side 321 and 322 is castellated (only two shown 321 a and 322 a). The tops of the castellations 321 a, 322 a on each side 321 and 322 are welded to the sidewalls 315 and 316 respectively, to form spaces (only two shown 321 b and 322 b) between adjacent castellations.

[0080] An inner housing 323 is arranged in the housing 314 and extends upwardly through the slot 319. Parts of the inner housing 323 are shown in FIGS. 3B to 3E. The inner housing 323 comprises a bottom plate 324, a body 325, a neck 326 and a top 327. The body 325 comprises a top plate 328 and two side plates 329 and 330. The side plates 329 and 330 may be welded to the top plate 328 or formed integrally with the top plate 328. The side plates 329 and 330 have castellations 331 and recesses 332 therebetween, as shown in FIG. 3C. The bottom plate extends substantially the entire length of the housing 314 and is welded to the casstellations 331. The neck 326 extends from the centre of the top plate 328 and has a top 327 arranged thereon to form a T-bar. The top 327 may be welded or formed integrally with the neck and the neck may be welded or formed integrally with the top plate 328. The neck 326 has a portion 333 locate near an end 334 of the top plate 328 which is not provided with a top and is chamfered. There is a ledge 335 provided at the end 334. The top 327 extends from the top of the chamfered portion 331 to a rear end 336 of the top plate 328. The top 327 is provided with an arrow head portion 341. The body 325 has an opening 337 for receiving a hose 338.

[0081] Referring back to FIG. 3, the castellations 331 in the body 325 of the inner housing 323 are vertically slideably arranged in the spaces 321 b and 322 b formed between the plate 320, the castellations 321 a and 322 b and the respective sidewalls 321 and 322 of the housing 314. The neck 326 is vertically slideably arranged in the slot 319 in the housing 314. An inflatable bladder 339 is fixed to the bottom face of the plate 320 and is linked to the hose 338. Return springs (340, only one shown) are spaced along the length of the central clamp 314 between the bottom plate 324 of the inner housing 323 and the bottom plate 316 a of the outer housing 314.

[0082] Referring to FIGS. 3F to 3K, the screen assembly 400 comprises a panel 401 made from steel, aluminium or plastics material having a plurality of triangular apertures 402 between two imperforate side areas 403 and (not shown). A layer of screening material 404, such as wire mesh is adhered to the panel 401 using a hot melt glue, powder adhesive, staples, sewing material or other means. The layer of screening material 404 may comprise one, two or three more layers of wire mesh.

[0083] The panel 401 is welded to a plurality of elements to form a support 405. Although, the support 405 may at least partly be made integrally with the panel 401 by folding portions of the panel 401, as disclosed in PCT Publication No. WO 01/76719 and herein above with reference to FIG. 3G. The plurality of elements comprises two side strips 406 and 407 which are welded to sides of the panel 401. A rear end 408 of the panel 401 has a strip of steel 410 welded thereto which has a bottom portion folded inwardly and downwardly to form a lip 409 for abutting another screen assembly provided with a lap. A front end 411 of the panel 401 has a strip of steel 412 welded thereto and has a bottom portion folded outwardly and folded back on itself to form a lap 413. A plurality of ribs 414 arranged between sides 406 and 407 are welded to the panel 401 and to the sides 406 and 407. Each rib 414 takes the form of a “lazy 7”, which increases its rigidity. It is an aspect of the invention to have a screen assembly comprising at least one rib which is formed in the shape of a lazy 7 to increase the rigidity of the screen assembly. The ribs 414 may be arranged along solid parts of the panel 401, so that the apertures 402 are not obscured.

[0084] A rail 416 is arranged along a central line of the screen assembly 400 in central recesses 415 in the ribs 414 and the strips of steel 410 and 412. The rail 416 is welded to the ribs 414 and strips of steel 410 and 412. The rail 416 is of uniform section and extends the entire length of the screen assembly 400. The rail 416 comprises a top 417, sides 418 and 419, each side having an inwardly and upwardly turning part forming a slot 420 and two shoulders 421 and 422. The shoulders 421 and 422 are flush with the bottoms of the ribs 414 and the steel strips 410 and 412. It should be noted that, it is preferred that the top 417 of the rail 416 is spaced from the panel 401, such that, in use, material filtered through the layers of screening material 404 and the apertures 405 in the panel 401 is substantially unobstructed and passes around the rail 416 and into a sump therebeneath.

[0085] Referring now to FIGS. 3L and 3M, in use, the front end of the slot 420 of the rail 416 of the screen assembly 400 is located over the chamfered neck 333 of the central clamp 311 and the sides 406 and 407 of the screen assembly 400 are located in the C-shape rails 306 and 307. The screen assembly 400 is slid on to the T-bar 326, 327 and into the C-shape rails 305 and 306 until the front of the screen assembly 411 abuts a preceding screen assembly or the end fitting of the shale shaker 400. A second, third, fourth and fifth screen assembly may be slid into the shale shaker 300 behind the first screen assembly 400 depending on the size of the shale shaker and the size of the screen assemblies, or in separate sets of C-shape rails provided on separate levels of the shale shaker, such as in Varco™ Brandt™ VSM 300™ or the King Cobra™ shale shakers. Once the screen assemblies are in place, the inflatable bladders 307, 308 and 339 are inflated. The bladders 307, 308 and 339 may be inflated simultaneously or one after the other. The sides of the screen assembly 403 are pushed down on to the bottom of the C-shape rail 305 and 306 by inflation of the bladders 307 and 308 and the rail 416 and hence the centre of the screen assembly is pulled down on to the shoulder 317 of the housing 314. It is preferred that the screen assembly and screening material thereon is now flat, although the screen assembly may be crowned or have an inverse crown. To remove the screen assemblies from the shale shaker, the bladders 307, 308 and 339 are deflated. Bladders 307 and 308 release the sides of the screen assembly 400. Return springs 340 are biased to expand and push the inner housing 323 upwardly in the outer housing 314 pushing the T-rail up and releasing engagement with the rail 416 in the screen assembly 400.

[0086]FIG. 4 shows an alternative embodiment of a screen assembly 500 and an alternative part of a central clamp (not shown in full), which may be the central clamp of FIG. 3 or FIG. 5. A rail 501 is arranged along a central line of the screen assembly 500 in central recesses 502 in ribs and the strips of steel 503 (and not shown). The rail 501 is welded to the ribs and strips of steel 503 (and not shown). The rail 501 is of uniform section and extends the entire length of the screen assembly 500. The rail 501 comprises a top 504, sides 505 and 506, one side having an inwardly and upwardly turning part 507 which is along the central line of the screen assembly, forming a hook a shoulder. The shoulder is flush with the bottoms of the ribs and the steel strips 503. It should be noted that, it is preferred that the top 504 of the rail 501 is spaced from an apertured panel 508, such that, in use, material filtered through the layers of screening material (not shown) and the apertured panel 508 is substantially unobstructed and passes around the rail 501 and into a sump therebeneath. A hook rail 509 of the central clamp, is shown engaged with the rail 501 for pulling the rail 501 and hence a central part of the screen assembly down to fix the screen assembly in place in the vibratory separator.

[0087]FIG. 5 shows an alternative for of a screen assembly 600 and an alternative part of a central clamp (not shown in full). A rail 601 is arranged along a central line of the screen assembly 600 in central recesses 602 in ribs (not shown) and the strips of steel 603 and (not shown). The rail 601 is welded to the ribs and strips of steel 603 and (not shown). The rail 601 is of uniform section and extends the entire length of the screen assembly 600. The rail 601 comprises a top 604, sides 605 and 606, each side having an inwardly and upwardly turning part 607 and 608 forming two shoulders and a slot 609. The shoulders 607 and 608 are flush with the bottoms of the ribs and the steel strips 603. It should be noted that, it is preferred that the top 604 of the rail 601 is spaced from an apertured panel 610 arranged on the ribs and steel strips 603, such that, in use, material filtered through the layers of screening material (not shown) thereon and the apertured panel 610 is substantially unobstructed and passes around the rail 601 and into a sump therebeneath. The central clamp comprises a gear wheel 611 attached to a motor (not shown), which may be electric, hydraulic or pneumatic, which turns the gear wheel. The gear wheel has teeth 612 which mesh with teeth 613 provided on a vertical member 614 held in a guide 615. The vertical member 614 has a neck 616 formed integrally with a T-bar rail 617, which engages with the rail 601. The neck 616 is located in a guide comprising shoulders 618 and 619. In use, the screen assembly 600 is arranged in the vibratory separator as described with reference to FIG. 3. The central clamp is operated by activating the motor (not shown), which turns the gear wheel 611 anticlockwise to pull the T-bar rail 617 downwardly. The shoulders 607 and 608 of the rail 601 abut the shoulders 618 and 619 to fix the screen assembly 600 in the vibratory separator.

[0088] It is envisaged that the basket, solid steel plates and rigid steel tubes could be made from any other suitable material, such as aluminium, carbon fibre, steel.

[0089] It is envisaged that the bladders may be inflated with a hydraulic fluid or a part pneumatic, part hydraulic system. It is also envisaged that the C-shape rail 307 and 308 about the periphery of the basket may be replaced by a hook strip arrangement.

[0090] The central clamp may extend the entire length of the vibratory separator or may extend the length of each screen assembly. 

1. A vibratory separator comprising a basket and a side rail for fixing at least a portion of a periphery of a screen assembly to said basket, characterised in that the vibratory separator further comprises means for pulling a screen assembly down within a periphery of a screen assembly to fix a screen assembly in said basket.
 2. A vibratory separator as claimed in claim 1, wherein said means is pneumatically operable.
 3. A vibratory separator as claimed in claim 1, wherein said means is hydraulically operable.
 4. A vibratory separator as claimed in claim 1, wherein said means comprises an inflatable bladder.
 5. A vibratory separator as claimed in claim 1, wherein said means is mechanically operable.
 6. A vibratory separator as claimed in claim 1, wherein said means comprises a rail for engaging a screen assembly.
 7. A vibratory separator as claimed in claim 6, wherein said rail is T-shaped.
 8. A vibratory separator as claimed in claim 1, wherein said means comprises an outer housing and an inner housing, said inner housing movable with respect to said outer housing for pulling a screen assembly downwardly to fix a screen assembly in said basket.
 9. A vibratory separator as claimed in claim 6, wherein said rail is attached to said inner housing and said outer housing comprises a slit through which part of said rail passes.
 10. A vibratory separator as claimed in claim 8, wherein an inflatable bladder is arranged in said inner housing for moving said inner housing with respect to said outer housing.
 11. A vibtratory separator as claimed in claim 10, wherein said outer housing has an intermediate member which passes through openings in said inner housing, said inflatable bladder arranged underneath said intermediate member.
 12. A vibratory separator as claimed in claim 8, wherein said vibratory separator has a length, said inner housing and said outer housing extends substantially said length of said vibratory separator.
 13. A vibratory separator as claimed in claim 6, wherein said vibratory separator has a length, said rail extends substantially said length of said vibratory separator.
 14. A vibratory separator as claimed in claim 1, wherein said basket is rectangular having a pair opposing side walls, said side rails arranged on each of said pair of opposing side walls.
 15. A vibratory separator as claimed in claim 14, wherein said basket comprises at least one beam linking said pair of opposing sides, said means arranged on said at least one beam.
 16. A vibratory separator as claimed in claim 1, further comprising a shoulder located within said periphery on to which said screen assembly is pulled on to to fix a screen assembly in said basket.
 17. A vibratory separator as claimed in claim 16, wherein said means comprises a stationary part which forms said shoulder or land.
 18. A vibratory separator as claimed in claim 1, wherein said means comprises a return mechanism to release a screen assembly.
 19. A vibratory separator as claimed in claim 18, wherein said return mechanism comprises at least one return spring.
 20. A vibratory separator as claimed in claim 1, wherein a bladder is arranged in said side rail.
 21. A screen assembly for a vibratory separator, the screen assembly comprising a support and at least one layer of screening material, wherein said screen assembly has a periphery characterised in that said support further comprises a fitting within said periphery, said fitting for receiving a means for pulling the support downwardly and fixing the screen assembly in the vibratory separator.
 22. A screen assembly as claimed in claim 21, wherein said fitting comprises a rail.
 23. A screen assembly as claimed in claim 21, wherein said screen assembly has a length and said rail extends the length of said screen assembly.
 24. A screen assembly as claimed in claim 22, wherein said rail is in the form of a T.
 25. A screen assembly as claimed in claim 22, wherein said rail is a channel.
 26. A screen assembly as claimed in claim 21, wherein said fitting is centrally mounted.
 27. A screen assembly as claimed in claim 21, further comprising a pull down member engageable with said fitting, said pull down member having arms, which in use, are engageable in clamping rails of a vibratory separator, such that upon activation of the clamping rails, the arms push the pull down member downwardly, pulling the support downwardly and fixing the screen assembly in the vibratory separator.
 28. A screen assembly as claimed in claim 27, further comprising a rigid chassis having a plurality of ribs, each of which forms a shoulder, in use said support is pulled down and fixed on said shoulders.
 29. A screen assembly as claimed in claim 21, wherein said support comprises a panel having apertures therein.
 30. A screen assembly as claimed in claim 29, further comprising a rigid chassis, said fitting formed in said rigid chassis, spaced from said at panel, such that in use filtered material flows therearound.
 31. A screen assembly as claimed in claim 29, wherein said panel comprises folded portions.
 32. A screen assembly as claimed in claim 31, wherein said at least one layer of screening material is adhered to said side portions of said panel.
 33. A screen assembly as claimed in claim 29, wherein said at least one layer of screening material is adhered to said area provided with apertures.
 34. A screen assembly as claimed in claim 1, wherein said at least one layer of screening material comprises at least a first layer of screening mesh arranged on top of a second each other, wherein said mesh size of said second layer is the same or larger that of said first layer and has larger diameter wires making up the mesh.
 35. A screen assembly as claimed in claim 34, further comprising a third layer of screening mesh.
 36. A screen assembly as claimed in claim 29, wherein said panel is flexible.
 37. A vibratory separator comprising a screen assembly as claimed in claim 21, the vibratory separator further comprising a basket, a vibratory mechanism and a clamping mechanism for fixing the screen assembly to the basket.
 38. A vibratory separator as claimed in claim 33 wherein said clamping mechanism comprises a pneumatic means.
 39. A vibratory separator as claimed in claim 35, wherein said pneumatic means comprises a pneumatic hose.
 40. A method for fitting a screen assembly in a vibratory separator, the screen assembly comprising a support having at least one layer of mesh arranged thereon, the method comprising the steps of inserting the screen assembly into a clamping mechanism of a vibratory separator, operating the clamping mechanism wherein at least part of said screen assembly within its perimeter is pulled down to fix said screen assembly in said vibratory separator.
 41. A method as claimed in claim 40, wherein the screen assembly further comprises a pull down member, the method further comprising the step of operating the clamping mechanism depresses a pull down member, pulling intermediate parts of said panel on to said support structure. 